In certain applications packers such as line top packers may need to be in a wellbore for days while being repositioned to accommodate other procedures. During this time the running tool that will ultimately set the packer is used to reposition the packer and the liner associated with the packer. When the time comes to set such a packer the running tool is released from the assembly, then picked up relative to the packer to allow spring loaded dogs to extend above the packer tieback extension so that a subsequent setting down weight will push the tieback extension to set the packer. The problem in some environments where the wellbore fluid has fine grit or solid particles is that in the course of the time that the packer is manipulated in the well before it is set the fine debris in the drilling mud can migrate into the setting sleeve and foul the spring-loaded dog mechanism to the point that the dogs will not extend when pulled free of the tieback extension and subsequent setting down weight will not set the packer because such force will not be transmitted to the tieback extension. If the debris accumulation is severe enough within this annulus, it can also cause difficulty even achieving this upward movement of the setting tool, and prevent release of the workstring (drill pipe or tubing) from the liner assembly.
Prior designs have recognized the need to exclude debris from the setting sleeve to avoid fouling the spring loaded dog mechanism and have approached the problem with two split segments that are attached to each other and span over a part of the annular gap between the setting tool mandrel and the tieback extension of the packer. This solution has not been optimal because where the grit in the mud is rather fine there was still solids migration beyond the barrier and the setting dogs jammed in the retracted position when pulled out of the tieback extension rather than springing out so that on setting down they could bear on the top of the tieback extension for setting the packer.
U.S. Pat. No. 7,604,048 developed a folding debris barrier 30 that was set after the packer set by the application of a further set down weight. It remained retracted with the packer unset and is thus not a workable solution to a situation of long term grit exposure in an unset condition as is envisioned for the debris barrier needs for the present packer application.
Another solution for sealing a mandrel in a seal bore is offered in US Publication 20110168387 is to use a foam material that fully spans an annular gap and is reported to enable pressure equalization through the open structure of the foam. The potential problem with this design is that it may plug with particulates internally and will fail to equalize pressure. The material can also have temperature and mechanical strength issues that could preclude using it for packer setting sleeve purposes in harsh grit-laden environments.
Packer cups have been used as debris barriers and have been oriented uphole to accumulate debris within the cup. Such orientation prevents pressure equalization from above to below the uphole oriented packer cup. Some examples of such a design are: US Publication 2003/0089505; WO2010/097616; U.S. Pat. Nos. 7,604,050; 7,540,323 and 7,011,157. Some designs allow for pressure equalization through debris catching packer cups by putting holes or ports in them or exposing mandrel ports near such packer cups, such as U.S. Pat. Nos. 7,882,903; 6,186,227; US Publication 2008/0314600 or US Publication 2007/0062690.
Combination pressure and vacuum devices have been used for large storage tanks that are responsive to relieve internal pressure and vacuum in the storage tank as it is filled or emptied. Such designs are shown in FIG. 4 in U.S. Pat. No. 6,019,126 but are too large and unwieldy for subterranean use and are not built to withstand the pressures normally seen in subterranean wellbores.
What is needed and provided by the present invention is a debris barrier that has the capability of pressure equalization as the tool is delivered so that a zone that starts at atmospheric pressure when run into the wellbore can equalize with well hydrostatic as such hydrostatic pressure increases with additional depth for the tool. The same barrier that allows such pressure equalization also has the capability of excluding even fine grit by its self energizing configuration after pressure equalization has occurred. If there is a failure of the equalization feature a dual acting rupture disc is provided. In one direction it can prevent collapse of the downhole tool due to large pressure differentials by letting the hydrostatic pressure rupture the disc inwardly to relieve the high differential pressure before the setting sleeve collapses. In some instances the packer has to be removed without being set and while it is still attached to the running tool. This can create a volume of trapped high pressure that can injure surface personnel if that pressure is not relieved before component disassembly. The dual acting rupture disc responds to a growing differential from within the tool to the surrounding annulus as the tool is removed from the wellbore. At some depth the differential as between inside the tool and the surrounding annulus is high enough to burst the disc in the outward direction toward the annulus. That way when the packer comes out of the hole there is no trapped pressure inside. These and other aspects of the present invention will become more readily understandable from a review of the detailed description and the associated figures while understanding that the full scope of the invention is to be found in the appended claims.